Trent Dilfer will start for the San Francisco 49ers on Sunday in place of quarterback Alex Smith, who has acknowledged a serious arm injury has been affecting his play.

With 49ers quarterback Alex Smith suffering from a shoulder injury, Trent Dilfer will start in his place this week against the Rams. A look at both quarterbacks this season.

Dilfer, the 14-year veteran who started two games for Smith earlier this season, got the assignment Thursday from coach Mike Nolan.

Smith and his coach had a lengthy meeting on Wednesday following the quarterback’s public disclosure that his recently separated right shoulder led to a forearm injury that prevents him from throwing well. Smith and Nolan both had previously denied Smith’s arm injury was causing his poor play.

So the 49ers (2-7) will turn to Dilfer for their home game against the St. Louis Rams (1-8).

“There’s no time for me to be sympathetic (toward Smith),” said Dilfer, who has a close relationship with the former No. 1 draft pick. “My job is to go out and play the best football I can play. … My relationship with Alex won’t change, but I don’t have time for that drama or any other type of drama.”